A multidisciplinary research team at the National
Institute of Standards and Technology (NIST) has found* that an organic
semiconductor may be a viable candidate for creating large-area electronics,
such as solar cells and displays that can be sprayed onto a surface as easily
as paint.

This airbrush technique deposits a well-studied material called P3HT to create spray-on transistors, which perform comparably to lab-standard equivalents made by spin coating. Credit: NIST

While the electronics will not be ready for market anytime soon, the research
team says the material they studied could overcome one of the main cost hurdles
blocking the large-scale manufacture of organic thin-film transistors, the development
of which also could lead to a host of devices inexpensive enough to be disposable.

Silicon is the iconic material of the electronics industry, the basic material
for most microprocessors and memory chips. Silicon has proved highly successful
as a substance because billions of computer elements can be crammed into a tiny
area, and the manufacturing process behind these high-performance chips is well-established.

But the electronics industry for a long time has been pursuing novel organic
materials to create semiconductor products—materials that perhaps could
not be packed as densely as state-of-the-art silicon chips, but that would require
less power, cost less and do things silicon devices cannot: bend and fold, for
example. Proponents predict that organic semiconductors, once perfected, might
permit the construction of low-cost solar cells and video displays that could
be sprayed onto a surface just as paint is.

“At this stage, there is no established best material or manufacturing
process for creating low-cost, large-area electronics,” says Calvin Chan,
an electrical engineer at NIST. “What our team has done is to translate
a classic material deposition method, spray painting, to a way of manufacturing
cheap electronic devices.”

The team’s work showed that a commonly used organic transistor material,
poly(3-hexylthiophene), or P3HT, works well as a spray-on transistor material
because, like beauty, transistors aren’t very deep. When sprayed onto
a flat surface, inhomogeneities give the P3HT film a rough and uneven top surface
that causes problems in other applications. But because the transistor effects
occur along its lower surface—where it contacts the substrate—it
functions quite well.

Chan says the simplicity of spray-on electronics gives it a potential cost
advantage over other manufacturing processes for organic electronics. Other
candidate processes, he says, require costly equipment to function or are simply
not suitable for use in high-volume manufacturing.